128 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
Group — Akiixa. 
Arius pidada. 
As the genus Arius, of all the genera of Silurold Fishes the most cosmopolitan in 
its geographical distribution, not only includes a considerable number of species, but 
is also fairly typical of several other genera in so far as the modifications of the 
anterior vertebrae and the structure of the air-bladder are concerned, we venture to 
give a detailed account of these structures in the Javan species, Arius pidada. 
The series of rigidly interconnected anterior vertebrae includes the first, the complex, 
and the fifth, sixth, and seventh vertebrae, all of which are also firmly connected with 
the skull, partly by reason of the anchylosis of the accessory articular processes of the 
basioccipital and complex centrum, and partly by the extension of a pair of bony 
laminae between the supraoccipital and the modified transverse processes of the fourth 
vertebra. 
Kelatively to the normal centra the body of the first vertebra is very small, and 
though visible in the fioor of the neural canal, of which its dorsal surface forms 
a part, is hidden ventrally by the coalescence of the accessory articular processes of the 
basioccipital and complex centrum ; laterally, it is to a slight extent visible on the 
exterior, wedged in between the complex centrum and the base of the skull (figs. 45 
and 46, v.^). The complex centrum is much elongated and has its posterior concavity 
deeper than the anterior (fig. 46, c.c.). Two pairs of nutrient foramina are visible on 
its ventral surface, in the roof of the aortic canal, which belong to the third and 
fourth vertebrae respectively (fig. 46). The body of the fifth vertebra {v.^) is smaller 
than the complex centrum which, however, it resembles in having the posterior 
concavity much deeper than the anterior. The sixth centrum is somewhat larger 
than the seventh but both are normal, except that their lateral surfaces are invested 
by the superficial ossifications (y.*^, v."‘). The eighth vertebra is normal and free 
(figs. 45 to 47, v.^). 
The neural arches of all the anterior vertebras from the complex to the seventh 
inclusive, are partially anchylosed together, only faint indications of sutures being 
observable between them (fig. 46). 
The neural spines of the third and fourth vertebras are long and stout ; the former 
is inclined forwards over the neural canal in the region of the first vertebra, and 
abuts against the supraoccipital and exoccipitals, but a small amount of intercalated 
cartilage still persists in a cleft in its anterior margin (fig. 46, a .5.®); the latter, on 
the contrary, is directed obliquely backwards and cleft at its distal extremity, and 
grooved along its posterior margin for the support of the two large anterior inter- 
spinous bones of the dorsal fin (n.s.'^). The spines of the four succeeding vertebra) 
are obsolete. The ninth vertebra has a pair of rudimentary spines and the tenth 
and following vertebne large spines, which are bifid in the region of the dorsal fin 
(fig. 46). 
